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TECHNICAL PAPERS

Effect of Wall Roughness on the Dynamics of Unsteady Cavitation

[+] Author and Article Information
Olivier Coutier-Delgosha1

 ENSTA - UER de Mécanique Chemin de la Hunière, 91761 Palaiseau Cedex, Franceolivier.coutier@lille.ensam.fr

Jean-François Devillers2

 ENSTA - UER de Mécanique Chemin de la Hunière, 91761 Palaiseau Cedex, FrancedevilJF@aol.com

Mireille Leriche

 ENSTA - UER de Mécanique Chemin de la Hunière, 91761 Palaiseau Cedex, Franceleriche@ensta.fr

Thierry Pichon

 ENSTA - UER de Mécanique Chemin de la Hunière, 91761 Palaiseau Cedex, Francepichon@ensta.fr

1

Now at ENSAM Lille ∕ LML Laboratory, 8 bld Louis XIV, 59046 Lille cedex, France

2

Now Scientific Consultant, 4 rue Mirabeau, 91120 Palaiseau, France

J. Fluids Eng 127(4), 726-733 (Apr 01, 2005) (8 pages) doi:10.1115/1.1949637 History: Received April 13, 2004; Revised March 27, 2005; Accepted April 01, 2005

The present paper is devoted to the experimental study of unsteady cavitation on the suction side of a two-dimensional foil section positioned in a cavitation tunnel with a small incidence angle. When the pressure is decreased in the tunnel, a sheet of cavitation characterized by large amplitude fluctuations is obtained on the foil. The present study focuses on the effects of the foil wall roughness on the cavity unsteady behavior. Four different sizes d of irregularities have been tested, from the smooth surface to a 400μm grain size. The characteristic frequency of the flow unsteadiness is investigated by analyzing the data measured by a pressure transducer mounted flush on one vertical wall of the test section, whereas the mean cavity length is obtained by visual measurements on the foil side. Several types of cloud cavitation are identified in the case of the smooth surface. The effect of roughness is a significant decrease of the cavity length and a large increase of the oscillation frequency. It results in Strouhal numbers higher than the classical values obtained for partial cavity fluctuations. Moreover, the cavitation cycle is disorganized by the increase of the roughness, as it can be detected by the fast fourier transform analysis of the pressure signal. The general effect is a reduction of the pressure fluctuation intensity.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 13

Strouhal numbers for various roughness and σ=0.9 (measurement set 1)

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Figure 14

Strouhal numbers for various roughness and σ=1.3 (measurement set 1)

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Figure 4

(a) Scheme of the adaptable foil section, and (b) view of the foil

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Figure 5

Detail of the roasted metal (microscope, magnitude 50) (a) Mean grain size 400μm, and (b) mean grain size 200μm

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Figure 6

Estimation of the cavity length from top and side views of the cavity (α=6deg,σ=1) (a) initial pictures, (b) postprocessing to visualize the limit of the cavity

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Figure 7

Comparison of the cavity lengths obtained (i) by direct measurements, (ii) by postprocessing of side and top views of the cavity

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Figure 11

Cavity lengths for roughness 400 and three values of σ (measurement set 1)

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Figure 15

Spectra of pressure signal fluctuations at incidence 5 deg and σ=1 with (a) a smooth surface (Lcav∕Lref=0.7) and (b) roughness 400 (Lcav∕Lref=0.55)

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Figure 16

Strouhal numbers for various roughness and σ=0.8 (measurement set 2)

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Figure 1

(a) Geometry of a rocket-engine turbopump inducer, (b) cavitating flow

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Figure 3

Vapor cloud shedding on the foil suction side (Incidence 3deg,Vref=6m∕s,σ=1)

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Figure 12

Evolution of the cavity length with the incidence for σ=0.8 and three different plates of various roughnesses (measurement set #2)

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Figure 8

Evolution of the maximum attached cavity length for several flow conditions and angles of attack varying from 2–6 deg (measurement set 1)

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Figure 9

Strouhal number associated with the cavity self-oscillation (measurement set 1)

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Figure 10

Evolution of the maximum attached cavity length on the foil equipped with the smooth plate (measurement set 1). The dashed line corresponds to the approximation curve plotted previously on Fig. 8.

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